Laminated glazing units provided with a transparent surface coating on one of the panes are often used in motor-vehicle construction and in architecture. In this case, the term “transparent” relates to the visible spectral range of light. The transparent surface coating serves for surface electrical heating or as a reflecting layer for a defined electromagnetic radiation spectrum, e.g., infrared radiation. In addition, the transparent surface coating is generally designed both as an electrically conducting multilayer film system using silver and as a functional layer and stop and antireflection dielectric layers. However, other constructions of layers are known. Since the thin film systems of the type mentioned are not generally corrosion resistant, they are included on the inside of a composite formed from glass and/or plastic panes. After inclusion of the film systems in a composite, though, a problem may arise because of the appearance of corrosion of the thin conducting layer at the peripheral edge of the laminated panes.
It is known from U.S. Pat. No. 5,131,967 to reduce the corrosion at the edge of a glass pane by removing the surface coating applied along its edge using a laser beam. The region removed has a width of about 0.025 mm to 3.2 mm. In this case, a line of separation may simply be produced in the surface coating at a short distance from the edge of the glass pane, or the layer of a peripheral region of the surface coating may be completely removed along the perimeter of the glass pane. The region stripped of the coating by laser treatment serves as a barrier, stopping the advance of corrosion which starts from the peripheral edge. During subsequent assembly of the glass panes using a film of adhesive, the surface included within the line of separation or the reduced surface at the edge is covered and sealed by the adhesive film, and thus protected from the environment.
Another solution to a problem that arises in a similar manner during manufacture of a glazing unit that is made of infrared-reflecting laminated glass of two individual glass panes is proposed in DE 195 03 510 A1. In the case of the laminated glazing unit described in that document, the infrared-reflecting layer does not lie on an individual pane, but instead on an additional carrier film. This carrier film is joined to two coating layers made of a thermoplastic in order to form the adhesive film which joins the two individual glass panes together. A flat piece corresponding to the shape of the glass panes, but smaller by a few millimeters, is cut out from the adhesive film at the edge. A precomposite is created from the flat piece of adhesive film and two glass panes that enclose it by removing the air between the adhesive film and the glass panes. A peripheral lateral slot remains between the glass panes and the peripheral edge of the adhesive film, and this lateral slot in the precomposite is filled by injecting, in a melt, the same thermoplastic as that of the coating layers of the adhesive films. The final assembly of the layers is then carried out during an autoclaving procedure.
The two aforementioned processes are effective but relatively expensive, since special plants such as a laser treatment station or an extruder must be available for the steps of the corrosion protection process. This machinery also is not usually available in the manufacture of laminated glazing units.
Despite these processes, there is a need for another process that is better suited to industrial manufacture of a laminated glazing unit provided with a corrosion-protected transparent surface coating. There also is a need for corrosion-protected laminated glazing units obtained according to such a process